In the field of bone surgery there is a need for bone replacement materials and implants which are compatible with the human body and easy to work with. To facilitate its growth in the body the bone implant should have a structure which is as similar as possible to that of bone. The implant material should thus be suitable as media for materials such as growth-promoting or growth-inhibiting substances, for example.
U.S. Pat. No. 3,929,971, to Roy, discloses synthetic materials which should likewise be made from the skeleton of corals, whereby it is proposed to design the process such that the resulting microstructure of corals mainly comprises either tricalcium phosphate (whitlockite) or hydroxylapatite.
A hydroxylapatite material, obtained from the calcium carbonate skeleton of lime-encrusting algae, has thoroughly proven itself as bone replacement material. Such a material is described in German Patent Number DE 37 09 897 C2, to Ewers et al. In order to mask the magnesium naturally present in the algae and to prevent the formation of β-tricalcium phosphate during production of hydroxylapatite material, fluoride is preferably added to the reaction mixture. For producing moulded articles the granular hydroxylapatite material obtained by hydrothermal synthesis is vibrated with dissolved lime as binder into a moulded article and then again subjected to hydrothermal treatment. The resulting bone implant has high interconnective porosity and a high specific surface. In its chemistry and crystalline structure it is substantially more similar to bones than other bone replacement materials.
Despite the excellent properties of the hydroxylapatite material described in German Patent Number DE 37 09 897 C2, to Ewers et al., it is desirable to have a bone replacement material available whose resorption in the organism is further improved and which leads to even faster formation of new bone. It has eventuated that hydroxylapatite material already has relatively good biological properties when supplied in the body, but that a lengthy biological decomposition has to be taken into consideration. This fact, in particular for hydroxylapatite materials with crystal sizes of the order of several micrometers with a Ca/P ratio of 1.67, is known from International Patent Application Number WO 97/17285 A1, from which issued U.S. Pat. No. 5,783,217, to Lee et al., and also from International Patent Application Number WO 94/02412 A1, from which issued U.S. Pat. No. 6,024,985, to Simkiss et al. But also for the hydroxylapatite materials known from German Patent Number DE 37 09 897 C2, to Ewers et al., in which the interconnective pore structure of the lime-encrusting algae remains intact, the biological decomposition period is greater than with tricalcium phosphate, for example. On the other hand, the biological decomposition period of tricalcium phosphate is substantially shorter. Most desirable is a biological decomposition period which is synchronised approximately with time, with which the bone regrows in place of the degraded bone replacement material. This results in the requirement for bone replacement material, where the decomposition period can be adjusted at least within certain limits during manufacture, thus stimulating accelerated bone formation without the material degrading too rapidly and accordingly without an interim period filled with connective tissue, for example, resulting.